Bonneaud et al U.S. Pat. No. 3,820,626 describes a manner of attenuating, in a selected preferred plane, the noise generated by jet engines and more especially by jets of what is called supercritical flow issuing from composite jet pipes by pinching such jets with the aid of two opposite panels, normally retracted during cruising flight but which can be deflected into a position where they pinch the jet and therefore its spreading in the said preferred plane where it is desired to obtain attenuation of the noise. In an advantageous example of the above which derives from the usefulness of being able to pass as desired from a silencer effect in the horizontal plane during the take-off period to a silencer effect in the vertical plane during flight over inhabited regions for example at the approaches to aerodromes, two orthogonal pairs of constricting panels are arranged each having its own control permitting the selective utilisation of one or the other of the said pairs in order to spread the jet into the desired one of the two orthogonal planes.
The object of the present invention is inter alia to effect the reduction of the losses occasioned by the use of constricting panels, while improving the degree of attenuation of the noise in the plane of spread of the jet.